Elemental sulfur is typically found naturally in salt domes, volcanic deposits, and some deposits of calcite, gypsum, and anhydrite. The Frasch Process is a well-known method for sulfur recovery in which molten sulfur is pumped directly out of the ground. In the Frasch Process, pressurized water is superheated to a temperature sufficient to melt or liquefy sulfur. The superheated water is introduced into beds of sulfur or into sulfur bearing rock deep in the earth through a system of pipes inserted into drilled holes. Molten sulfur is then pumped to the surface through a system of compressed air pipes. The Frasch Process is well-known for relatively inexpensive extraction of high purity sulfur. Sulfur deposits in volcanic rock, however, are typically not amenable to the Frasch Process. For instance, the efficiency of the Frasch Process is compromised when sulfur deposits are located near to the surface of the ground or when less concentrated deposits are dispersed in rock or other impurities. Such situations can be common in volcanic sulfur deposits.
Sulfur is typically extracted from volcanic deposits by mining the sulfur ore and “melting out” the sulfur from the ore. For example, using the Sicilian process, sulfur ore is ignited and a portion of the sulfur serves as a fuel source to heat and liquefy the remaining sulfur in the ore. The molten sulfur is then recovered and cooled. The Sicilian process, however, tends to be limited to certain types of sulfur deposits. In addition, burning the sulfur generates noxious gas byproducts and limits the amount of recoverable sulfur. Vaporization methods for sulfur extraction involve heating ground ore to a temperature sufficient to vaporize the sulfur and then extracting the sulfur gas. In an autoclaving method, superheated water and steam are used to liquefy the sulfur and then the liquefied sulfur is extracted. These and other methods of sulfur recovery are described in more detail elsewhere, such as in U.S. Pat. Nos. 4,923,482, 4,722,832, 5,096,571, and 3,939,256.
Conventional sulfur recovery methods typically involve melting, vaporizing, or otherwise converting sulfur into a molten state. Because molten sulfur tends to adhere to gangue and other impurities in the ore, the purity of the sulfur recovered by these methods can be limited and additional purification processing may be necessary. In addition, pressurized tanks and/or temperatures above the boiling point of water, typically between 120° C.-140° C., are needed to melt sulfur. Because heating and pressurizing steps are energy intensive and costly, sulfur extraction techniques have had limited success at efficiently recovering sulfur from volcanic deposits. Therefore, there exists a need for a more cost-effective method of sulfur extraction from sulfur ore.